1. Technical Field
The present invention relates to a method of driving a liquid crystal display device. More particularly, the present invention relates to a method of driving a liquid crystal display device with reduced voltage/current changes in response to a change of operating modes.
2. Related Art
Flat panel displays, such as liquid crystal display (LCD) devices, plasma display panels (PDP), field emission displays and electro-luminescence displays (ELD), replace displays using cathode ray tubes. In particular, LCD devices are in demand because LCD devices provide several advantages, such as a high resolution, a light weight, a thin profile, a compact size, and low power supply requirements.
LCD devices include two substrates that are spaced apart and face each other with a liquid crystal material interposed between the two substrates. The two substrates include electrodes that face each other. A voltage applied between the electrodes induces an electric field across the liquid crystal material. Light transmissivity of LCD devices may change by adjusting the intensity of the induced electric field, which may result in alignment change of liquid crystal molecules in the liquid crystal material. Thus, LCD devices display images by varying the intensity of the induced electric field.
LCD devices include a liquid crystal panel, a driving circuit and a backlight unit. The driving circuit provides data signals and control signals to the liquid crystal panel. The backlight unit provides light to the liquid crystal panel. LCD devices may include a power management unit that supplies voltages to the driving circuit and the backlight unit. The backlight unit and the driving circuit may be supplied with a voltage in common. The driving circuit may have different loads if an operating mode of LCD devices is changed. For example, an LCD device may operate in a normal display mode and may be changed to a reset mode, a standby mode, or a sleep mode. This change of modes may cause the load of the driving circuit to be changed. This load change may cause the backlight unit sharing the same voltage to have an abnormal voltage level. In particular, the load change may result from a plurality of capacitors. The driving circuit may include a DC-DC converter as one of its sub-circuits. The DC-DC converter generates DC voltages having various levels. The DC-DC converter includes the plurality of capacitors. When the operating mode is changed and each sub-circuit may stop to operate, the capacitors in the DC-DC converter may discharge charges simultaneously. Accordingly, charges discharged from the capacitors may flow to the backlight unit. As a result, the backlight unit may be supplied with higher voltages.
FIG. 1 is a graph illustrating abrupt voltage/current changes applied to a backlight unit in an LCD device. As shown in FIG. 1, an operating mode is changed at Timing T1. A voltage supplied to the backlight unit is level-jumped for an interval T2. A current I flowing in the backlight unit is changed abruptly for the interval T2. This abnormal current change may be caused by the load change in the driving circuit. As noted above, the load change results from the change of the operating mode. This abnormal current change may reduce life span of elements contained in the backlight unit. Further, a user may perceive a flicker on a display screen due to the increased brightness. Accordingly, there is a need of a driving method of a liquid crystal display device that minimizes abnormal voltage or current changes applicable to backlight units.